As well known to those skilled in the art, chlorofluorocarbon-based compounds conventionally used as foaming agents, abluents, aerosol propellants, and coolants, are known as materials with high ozone-depleting potential which destroy the ozone layer in the stratosphere, and so have been replaced with hydrochlorofluorocarbon (hereinafter, referred to sometimes as “HCFC”). However, recently, HCFC based materials are prone to be replaced with hydrofluorocarbon (hereinafter, referred to sometimes as “HFC”) compounds, without ozone-depleting potential, because HCFC-based materials still have ozone depleting potential, even though its value is low.
Difluoromethane (CH2F2, hereinafter referred to sometimes as “HFC-32”) is a substance used to replace chlorodifluoromethane (CHF2Cl, hereinafter referred to sometimes as “HCFC-22”). Conventional methods of producing HFC-32 are classified into a liquid phase method and a gas phase method. According to the conventional gas phase method, methylene chloride (CH2Cl2, hereinafter referred to sometimes as “HCC-30”) is reacted with hydrogen fluoride (HF) in gas phase at 350 to 500° C. in the presence of a fluorination catalyst to produce HFC-32. However, the conventional gas phase method is disadvantageous in that it is difficult to desirably control reaction conditions because of the high reaction temperature, side products are produced in great quantities to reduce yields of HFC-32, and complicated apparatuses are needed, thereby lowering reaction efficiency in comparison with the conventional liquid phase method.
As for the conventional liquid phase method, HCC-30 is reacted with hydrogen fluoride (HF) at 60 to 110° C. in the presence of an antimony pentachloride (SbCl5) catalyst. However, this conventional liquid phase method is disadvantageous in that super acid is undesirably produced under high temperature and pressure to corrode a reactor made of metals, thus shortening the reactor's life span. Efforts to solve the above disadvantage have been made, in which a concentration of a catalyst is reduced or the reactor is made of a corrosion-resistant metal, but the above disadvantage was not completely solved. Therefore, a reactor, an inner wall of which is lined with fluorine resin (polytetrafluoroethylene, hereinafter referred to as “PTFE”) is used to completely prevent corrosion of the reactor.
When HFC-32 is produced according to the conventional liquid phase method, it is necessary to continuously supply heat from an external heat source to a reactor so as to supply a reaction heat needed for the reaction. Hence, if the reactor lined with the PTFE resin and having a lower thermal conductivity than the metal reactor is used instead of the metal reactor, a separate heat supplying unit is additionally needed. In the case of the conventional gas phase method, super-heated hydrogen fluoride and HCC-30 in gas phase are fed into a reactor. However, these feeds are in a gas phase, so remaining in the reactor for a short time. Accordingly, super-heated feeds should be continuously and sufficiently fed into the reactor so as to maintain a desired temperature in the reactor. In other words, a great amount of super-heated unreacted feeds as well as feeds directly consumed in the gas phase reaction are needed so as to constantly maintain a reaction temperature. The unreacted feeds are separated from products by a heat exchanger, reheated, and fed into the reactor, thereby reducing energy efficiency.
Accordingly, there remains a need to develop a method of producing HFC-32 in high yield while securing energy savings.